Bacteria of the genus Salmonella are a group of gram-negative pathogens that cause a wide range of human diseases from localized gastroenteritis to typhoid fever and septicemia. Although significant progress has been made in understanding the mechanisms of Salmonella pathogenesis, more than 12 million cases of typhoid fever occur annually, and emerging antibiotic resistant strains pose a significant threat to human health. The overall goal of the proposed research is to understand how the non-receptor tyrosine kinase Focal Adhesion Kinase (FAK) functions in host defense against the enteric pathogen S. typhimurium. The experiments outlined herein provide an integrated approach to determine how this molecule affects Salmonella disease pathology through its impact on the innate immune response and the integrity of the intestinal epithelial barrier. In Specific Aim 1, we will determine how FAK expression by macrophages modulates the cellular immune response during Salmonella infection in vivo. We will accomplish this by examining bacterial colonization levels and inflammation in tissues derived from wildtype and myeloid-specific conditional FAK knockout mice. We will also examine the phagocytic capacity of FAK-deficient macrophages using advanced flow cytometric techniques. The studies described in this aim will elucidate how differences in the recruitment and/or function of phagocytes occurring in the absence of FAK impact the complex balance between host survival and death. While the presence of cytokines helps initiate and regulate the immune response to Salmonella, the appropriate balance between pro- and anti-inflammatory cytokines is essential to control infection and avoid damage to the host. In Specific Aim 2, we will investigate the FAK-mediated signaling pathways involved in macrophage-mediated cytokine production during Salmonella infection. To do this, we will first examine the ability of FAK-deficient macrophages to produce pro- and anti-inflammatory cytokines followed by an investigation into the specific signaling molecules involved in cytokine production. Finally, in Specific Aim 3, we will determine how FAK expression in the intestinal epithelium impacts host susceptibility to Salmonella infection. Using mice in which FAK is conditionally deleted from the intestinal epithelium, we will assess how the loss of this molecule from the epithelial barrier affects bacterial colonization levels in the small intestine and dissemination to distal tissues.